This invention relates generally to microwave circuits and to the fabrication thereof.
The state of the art in fabrication and construction of millimeter and sub-millimeter wave length microwave systems before the present invention was essentially a "bolt together" waveguide component technology. Individual circuits or discrete components were developed and then interconnected to provide the desired system. In essence, the "blocks" of the overall block diagram of the microwave system were assembled after each "block" was individually developed.
Various problems and shortcomings are inherent in the "bolt-together" approach. One such shortcoming is the high frequency limitation that exists when separate components are bolted together. The size and separation of individual components cannot be scaled proportionally for extremely short wave lengths, resulting in uncontrollable parasitic reactances which limit performance. Other difficulties inherent in the waveguide approach are bulkiness, excessive weight, and high manufacturing costs. In addition, minor design changes can result in costly hardware modifications.
The technology of electronic circuitry has evolved from discrete components such as diodes, transistors, capacitors, and resistors on printed circuit boards to the use of monolithic linear and digital integrated circuits. This trend has continued by combining specific integrated circuit functions into larger integrated circuits having versatile and multi-function capability such as in the case of electronic calculators, watches, and micro-computers.
Concurrently with these developments in electronic circuitry, similar techniques have been employed in the technology of microwave circuits. GaAs field effect transistors (FETs) have been developed as well as microwave integrated circuit components such as oscillators, mixers, amplifiers, detectors, and filters, using both monolithic and hybrid construction techniques. With the development of the micro-strip radiator, high performance monolithic micro-strip phased arrays have also been developed.
It has been recognized that there are advantages in performance and versatility to be gained by building micro-computer controlled antenna systems. Various multi-mode systems have been developed to demonstrate these advantages. In such systems, the electronics, comprising integrated circuits mounted on printed circuit boards were packaged separately and interfaced with an antenna by means of a multi-conductor cable. Such construction represents the present state of the art in microwave system fabrication. To date, complete microwave systems have not been fabricated as a monolithic unit.